In principle, an SMD production line consists of a printer and/or dispenser, a pick-and-place system and a reflow oven. Research projects often claim maximum quality at minimum batch sizes, which cannot be fulfilled by high-speed production lines. For such production, other solutions are required.

In most cases, semiautomatic production equipment is ideal. Most process parameters are controlled by the machine and, therefore, are reproducible. Programming and setup efforts are minimized because, for complex tasks, the process can profit from operator flexibility. Of course, there are highly flexible automatic machines on the market, too, that can meet the requested specifications for flexibility and quality. The following article describes the prerequisites that such machines must fulfill.

Printing or Dispensing?
The fastest and most precise way to create the finest solder paste structures is (and will be) printing with a stencil and squeegees. Even a semiautomatic printer such as the SP003 from Essemtec (Fig. 1) can produce excellent results. With its double squeegee, individually adjustable squeegee pressure and motorized print head, this machine controls the most important print parameters reproducibly. Even the parallel separation of stencil and substrate after printing is automated, and the printer can be equipped with a dual camera vision for easier stencil/substrate alignment.

Figure 1. Semiautomatic screen/stencil printer SP003-MLV with vision for ultra-fine-pitch printing.

For research and development, this type of printer will be adequate in most cases. More automation of the print process will not necessarily improve the quality, but certainly will increase reliability for larger series. If the print process itself is part of the research project, then the use of a fully automatic printer is indispensable. Only such machines can control the full process and reproduce it. For example, the Frauenhofer Institute, Germany, uses the SP600 automatic printer from Essemtec for the optimization of the thick film printing process. A leading personnel aircraft MFG in Kansas uses multiple SP600 printers for the highest quality solder paste printing for their electronics.

With small series, there often is the desire to avoid stencil manufacturing and to apply solder paste with a dispenser instead. Unfortunately, dispensing paste for the smallest components (0603 or smaller) or finest structures (pitch 0.6 mm or smaller) is very demanding. Standard dispensing valves such as a time/pressure or Archimedean Screw Valve will only deliver acceptable results for larger components and structures. For fine-pitch dispensing, specialized dispensing valves and pastes are required. The CDS-PFV Piezo Flow Valve from Essemtec is an example of such a valve. It has been developed especially for small-volume dispensing of pastes and filled liquids. With an adequate solder paste, it can dispense fine pitch down to 0.4 mm pitch, too. However, solder paste structures produced with a stencil printer are always more accurate and better suited for the SMD process than dispensed dots.

Semiautomatic Machines Often Are the Best Choice
The assembly of SMD components is very tolerant regarding deviations in the placement process itself. The quality of the solder joint more depends on the quality of the solder paste printing and the reflow process. For component assembly, however, it is important to place the right component at the correct place, respect the orientation, and to set all leads exactly into the printed or dispensed solder paste. To control all this, high tech is necessary — or a human being.

The semiautomatic pick-and-place system EXPERT-SAFP from Essemtec (Fig. 2) perfectly combines the strengths of a person and a machine. The system can be programmed with placement data just like an automatic pick-and-place machine. An integrated linear measuring system controls the pickup and placement position of each component. The motion, however, is executed by the human operator and guided by light and sound. The operator handles the SMD components with a vacuum needle just like an automatic machine, and is responsible for the fine alignment and the placement of the parts. Placement errors are not possible because the EXPERT controls operator motion and will ask for correction when it detects a deviation. 

Figure 2. Semiautomatic pick-and-place EXPERT-SAFP ideally combines the strength of machine and operator.

A semiautomatic EXPERT pick-and-place system enables top-quality production from series size 1. Programming and setup effort is minimal. The application spectrum of the machine is virtually limitless. In addition to SMD components, it also can be used for die attach or complete electronic modules assembly. The machine can be upgraded with a time/pressure dispenser for glue and solder paste, a Microplacer for BGA/microBGA/flip chip, etc., and a hot air tool for small soldering tasks on the component level. For special applications, these smart machines have been equipped with a placement force sensor. EXPERT systems are used, for example, by the CERN research institute in Geneva, Switzerland, or the University of Maryland in America.

For more complete placement, fully automatic pick-and-place machines such as the PANTERA, CSM or FLX Series from Essemtec can be used. Those machines provide intelligent feeders and vision systems and feature very quick changeover, and virtual placement and simulation tools. The FLX2011 (Fig. 3), a highly flexible automatic pick-and-place system, won a 2008 SMT China Vision Award in the category “Multi-Purpose Pick-and-Place.” A machine within the CSM series, the CSM7100V, is used for prototyping by A Major Commercial Aircraft MFG in Seattle, WA.

Figure 3. Highly flexible automatic SMD pick-and-place FLX2011, winner of the 2008 SMT China Vision Award in the “Multi-Purpose Pick-and-Place” category.

One Machine for Soldering and Curing
For today’s reflow, soldering machines should be used that also can process lead-free solder pastes. Simple infrared ovens are not capable of regulating the higher soldering temperatures with the required accuracy. To date, full convection reflow ovens, mixed-technology systems (convection with IR-support) or vapor phase systems should be chosen for the job.

For single PCB processing, a batch type reflow oven such as Essemtec’s RO-06 is a good solution. With its motorized drawer, it can automate the complete soldering process and the system requires only small space. However, in respect to energy consumption, such an oven only can be recommended for soldering a few PCBs because the process chamber must be heated up and cooled down for each soldering process.

Reflow ovens with a conveyor, such as the compact RO300FC from Essemtec (Fig. 4), are different: Each heating zone has time to stabilize on the desired temperature. This makes regulation of the temperature profile easier. Furthermore, temperature distribution is more even than inside a batch oven, which is especially important for processing complex and heavy PCBs because every component at every location should be soldered with the exact same temperature profile.

Figure 4. High quality full convection reflow oven with very small footprint: RO300FC.

The comparison between convection and vapor phase technologies is normally won by the first solution because of the lower price and the higher flexibility of a convection reflow oven. If the thermal zone separation of a convection system is good, then nearly every soldering or curing profile can be processed with such an oven. There is no need for changeover and only a little waiting time for zone stabilization is required. On the other hand, when using a vapor phase system, the complete process medium must be exchanged to make it ready for another application.

Local Machine and Process Specialist
Research institutes and universities most often use semiautomatic production systems from Essemtec because these devices feature a large application range and do not need much programming and setup effort. Such machines control the most important process parameters and reproduce them with high precision, guaranteeing maximum quality at the smallest series sizes. If the production process itself is part of the research, then it is a must to use fully automatic machines. Only those can fully reproduce a process.

Essemtec USA in Glassboro, NJ, is one of the largest suppliers of electronics production equipment for universities and research institutes in the US and Canada. Essemtec USA not only sells high-quality Swiss-made products but also is an experienced SMT process partner. Local support and service is available all over the country. Machine and process trainings are provided by qualified specialists with high levels of expertise and long-term experience in the production of electronics products. For evaluation and training purposes, a well-equipped showroom and process laboratory is available in Philadelphia, PA.

The Swiss machine supplier Essemtec is a leader in the area of flexible production systems for the electronics industry. The company has been designing, building and selling equipment for every step in the board assembly arena since 1991. For example, there are paste printers, dispensers, placement machines and soldering equipment. Manual, semi-automated and fully automated machines are available. The product portfolio also includes transport and storage systems, as well as software solutions for planning, simulation, optimization and documentation of the production processes.

Together with machine delivery, customers receive full access to the company’s remote maintenance system and to the customer portal MyEssemtec.com. Essemtec also offers attractive solutions for financing of capital investments and service contracts.

All Essemtec equipment is optimized for maximum flexibility. The user has the capability to change from one product to the other immediately on the shop floor and while simultaneously using the manufacturing capacity to its maximum. Essemtec – be more flexible. www.essemtec.com
 

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